The present invention relates generally to fuel cells, and more particularly to a fuel cell electrolyte and catalyst.
Fuel cells are devices that rely on electrochemical reactions to generate electrical current. Fuel cells operate upon oxidation of fuel. The fuel may be hydrogen or hydrogen-based compounds, such as methanol, alcohol, etc. A fuel cell includes an anode and a cathode, with an electrolyte in between the two electrodes.
One type of fuel cell is the proton-exchange membrane (PEM) fuel cell. In a PEM fuel cell, a catalyst in the anode splits the hydrogen into protons and electrons and the membrane further is capable of allowing just the protons to pass through to the cathode. Electrons must travel around the membrane and thus create an electrical current. The PEM fuel cell is simple, highly efficient, tolerant of impurities in the fuel, and can at least partially internally reform hydrocarbon fuels.
FIG. 1 shows a typical PEM fuel cell 100. Fuel such as H2 passes through the anode 103 and is split into protons (H+) and electrons (exe2x88x92) by the catalyst layer 104. The protons pass through the electrolyte layer 107 to the cathode 112, while the electrons travel through an external load circuit 115 and may perform electrical work. When the protons meet oxygen at the cathode 112, they combine to produce H2O. The output of the fuel cell 100 therefore is water and electrical current.
FIG. 2 shows a prior art catalyst layer 104 and electrolyte 107. The catalyst layer 104 is formed on the electrolyte 107, and typically comprises carbon particles that may be applied in a paste form. In the paste, the carbon particles are mixed with a binder dissolved in a solvent, wherein the binder hardens to form a relatively solid but porous structure of particles. Alternatively, in some prior art fuel cells, particles are sintered (heated) until they bond, forming a porous structure. As a result, the porosity of the prior art catalyst layer 104 is somewhat random and the porosity gives a large amount of surface area over which the H2 can react.
However, the prior art has several drawbacks. Platinum is a typical element used for the catalyst layer 104, and platinum is very expensive. The prior art approach to forming the catalyst layer 104 results in a relatively thick layer and is therefore wasteful and costly. In addition, the thickness of the prior art catalyst layer 104 results in a large distance for protons to traverse, which decreases the efficiency of the prior art fuel cell.
Therefore, there remains a need in the art for improvements in fuel cells.
An electrolyte for a fuel cell comprises an electrolyte body, a plurality of microstructures formed into or extending out of the electrolyte body, and thin film layers formed on the electrolyte body. A microstructure possesses a depth or a height and includes one or more sidewalls and a bottom surface. A sidewall of the microstructure advantageously creates a significant unobstructed diffusion area, wherein protons may travel laterally into or out of the electrolyte body. Therefore, when a proton is generated by the interaction of the fuel with a thin film layer, the proton may travel laterally only a short distance in order to enter or exit the electrolyte body, thereby improving the performance of the fuel cell.